The present invention generally relates to closed volume inflation devices. In particular, the present invention relates to inflation devices such as syringes used to inflate and deflate balloon catheters.
Balloon catheters are sometimes inflated with gas, rather than liquid, because the balloon can be inflated and deflated more quickly than a comparable volume of saline or other liquid inflation media. Gas inflation has proved particularly useful in inflation of balloon centering catheters used in radiation therapy, which relies on a centering balloon to prevent the radiation source from being too close to one side of the target vessel. The use of gas rather than liquid decreases the amount of attenuation of radiation between the radiation source and the vessel wall.
While gas filled balloons are advantageous in some situations, the prior art process of preparing an inflation device for gas inflation is much more complicated than that for liquid inflation. Although air would be relatively easy to load into an inflation device, air is not a suitable inflation medium, because air does not rapidly dissolve in blood. In the event that the balloon bursts or leaks, bubbles could be formed in the arterial blood, impeding blood flow. In addition, a chief component of air, nitrogen, is not desirable for balloon inflation because nitrogen gas has thrombogenic properties which may present clinical risks in the event that the balloon bursts. Accordingly, it is desirable to use a gas other than air and to prevent air contamination of the gas used. A preferable gas used for balloon inflation is carbon dioxide.
Many medical facilities have built-in plumbing systems that provide gases such as carbon dioxide. Alternatively, a pressurized gas canister of carbon dioxide may be used. In either case, the pressurized source of carbon dioxide must be connected to a reduction valve to fill the inflation device with gas. The reduction valve lowers the pressure of the gas to a pressure suitable for the syringe. The reduction valve may utilize several stopcocks that must be opened for the gas to flow. For example, a first stopcock may be located at the reduction valve, a second stopcock may be located at the catheter connection point, and a third stopcock may be located at the syringe. Such systems are physically cumbersome and unwieldy, and require considerable preparation time by skilled medical personnel. Accordingly, a desirable feature in an inflation device would be an inflation syringe preloaded with a specified gas which the physician could conveniently use without extensive preparation and equipment.
Unfortunately, however, the storage of gas in a syringe mechanism presents several difficulties. Most plastics used in syringe manufacture are gas-permeable, at least to some extent. In addition, most stopcocks and syringe plungers, even when manufactured to precise specifications, are subject to leakage over extended periods of storage. Finally, packaging materials used to maintain sterility are usually gas permeable to facilitate ETO sterilization. These factors contribute to loss of the stored gas and/or contamination of the stored gas by air.
The preloaded inflation device of the present invention is suitable for inflating and deflating a wide variety of balloon catheters such as a centering balloon catheter or an angioplasty balloon catheter. In addition, although described with specific reference to a syringe type inflation device for purposes of illustration, other closed volume inflation devices are within the scope of the present invention.
The present invention provides several embodiments of an inflation device preloaded with an inflation gas (other than air). As used herein, the term inflation gas refers to any gas, other than air, that is suitable for balloon catheter inflation such as carbon dioxide gas. The present invention also provides means for preventing air contamination of the inflation gas contained in the inflation device. In addition, the present invention enables the user to positively confirm that no air contamination of the inflation gas stored in the inflation device has occurred.
The present invention generally provides for an inflation device which is preloaded with an inflation gas, such as carbon dioxide gas, for balloon inflation. The inflation device is preferably preloaded by the manufacturer and/or packager of the inflation device. The inflation device generally has a body with a chamber preloaded with the inflation gas, and includes some means for preventing air contamination of the inflation gas. The means for preventing air contamination may vary according to the particular embodiment of the invention.
In a first embodiment of the present invention, a syringe is preloaded with a gas suitable for balloon inflation, such as carbon dioxide, and then placed in a container such as a pouch or envelope that has low gas-permeability. The container is filled with the same gas as that loaded into the syringe, at approximately the same pressure, after which the container is sealed. Because the container has low gas-permeability, air is not able to enter the container, or the syringe. Although the gas stored in the syringe may exchange with that in the container, there is no contamination since the gases are similar. After the container is sealed, the entire syringe and package may be sterilized with a non-gas based sterilization process, such as gamma or e-beam radiation, in accordance with existing techniques.
In another embodiment of the present invention, the syringe may contain within its main body a capsule of gas, the capsule being made of a gas-impermeable membrane. When the syringe is ready for use, the capsule may be broken or otherwise opened by piercing or cutting the membrane. For example, the capsule may be broken manually with a sterile pin. Alternatively, the syringe may contain a small pin or other sharp object pointing generally towards the proximal end of the syringe which punctures the gas capsule when the gas capsule is pressed forward by compression of the syringe plunger. In a preferred embodiment, the capsule is formed in a manner which does not interfere with the compression of the syringe plunger (i.e., the plunger will not get entrapped on the compressed capsule).
In a further embodiment of the present invention, the inflation gas is stored in a syringe that is sealed by a membrane, preferably located at the distal opening of the syringe. Although the gas contained within the syringe may pass in minute quantities through the plunger seal, the distal sealing membrane, or the syringe body itself, particularly if the syringe tubular body is constructed of a plastic material which is gas-permeable, air contamination is detectable by having a-nitrogen-sensing strip packaged within the syringe. When the syringe is to be used, the membrane at the distal opening of the catheter may be cut, punctured, or otherwise opened. With this embodiment, a small strip is treated or coated with a chemical that changes appearance (e.g., color) in the presence of an unacceptable amount of nitrogen gas. A nitrogen sensing strip may also be disposed in the pouch containing the syringe in the first embodiment. At the time of use, the color of the strip may be checked to ensure that an unacceptable amount of air has not infiltrated the syringe.